Glare is one of the troublesome factors when driving a vehicle. Many efforts have been made to solve the glaring problem. One of the most effective ways is to provide an electrochromic unit for the rearview mirror of the vehicle. The electrochromic unit deepens the color and thus reduces the reflectance of the mirror according to the degree of the glare, thereby minimizing the glaring effect.
FIG. 1 is a schematic diagram showing a conventional anti-glare rearview mirror. A photo-detector 1 is mounted on an electrochromic rearview mirror 2, and oriented to detect rearward light. The photo-detector 1 outputs a control signal to the electrochromic rearview mirror 2 to adjust the reflectance of the mirror 2 according to the intensity of the rearward light. For example, for an intense rearward light, the reflectance of the mirror 2 is required to be lowered. That is, the color of the mirror 2 is deepened in order to avoid irritating to the driver's eyes.
The electrochromic unit receives a voltage from a voltage source which is the ignition or the vehicle battery voltage. The voltage is reduced to a level suitable for the electrochromic purpose, e.g. a voltage ranged between 0 and 3.5V. The higher the voltage level is applied to the electrochromic unit, the deeper the color of the mirror is, and the lower the reflectance of the mirror becomes. The reflectance is lowered from an uncolored initial level, e.g. 55% in general.
In this electrochromic mechanism, the rearward light is not necessarily glaring light. For example, in the sunny daytime, little glare effect is rendered and no reflectance adjustment is required. The electrochromic rearview mirror 2, however, is still frequently adjusted in response to the light detected by the photo-detector 1 according to this conventional anti-glare mechanism. As is known, the electrochromic unit of the mirror 2 has a certain life span, i.e. certain color-change cycles, the unnecessary reflectance variation will speed up the consumption of the electrochromic unit. Furthermore, since the photo-detector 1 is oriented to a certain direction and has a confined detection range α, the glare situation beyond the detection range α cannot be detected and solved.
FIG. 2A is a schematic block diagram showing another conventional electrochromic rearview mirror system. The rearview mirror system includes an interior rearview mirror assembly 11 inside the vehicle, two exterior rearview mirror assemblies 12 and 13 by two sides of the vehicle, respectively, and a control device 14. Each of the rearview mirror assemblies 11, 12 and 13 includes an electrochromic unit 111, 121, 131 which performs color change of the mirror under the control of the control device 14.
Further referring to FIG. 2B, the control device 14 includes a forward light sensor S1, a rearward light sensor S2, a voltage source 141, a micro-controller 142 and a drive circuit 143. The sensors S1 and S2 are disposed at the forward and rearward sides of the interior rearview mirror assembly 11 for detecting the intensities of the forward light and rearward light, respectively. First of all, the micro-controller 142 determines whether it is daytime or nighttime according to the forward light intensity detected by the sensor S1. For example, when the intensity of the forward light is detected to be greater than 50 Lux, it is determined to be daytime, and the micro-controller 142 disables the drive circuit 143. On the contrary, if the forward light is no greater than 50 Lux, the drive circuit 143 is enabled to adjust the reflectance of the mirrors according to the intensity of the rearward light in a manner as mentioned above. This conventional anti-glare mechanism, in spite of saving unnecessary operation cycles of the electrochromic units, may still waste many cycles under sufficient ambient illumination in the nighttime. Moreover, since the above-mentioned electrochromic mechanism does not work in daytime, the glaring effect resulting from intense sunrise or sunset sunlight cannot be avoided.
A further anti-glare mechanism was developed to solve the above problems by comparing the rearward light with ambient light. FIGS. 2 and 3 are referred to illustrate this mechanism. The micro-controller 142 determines whether a glaring situation occurs in response to the light intensity difference detected by the forward sensor S1 and the rearward sensor S2, and controls the drive circuit 143 to apply a suitable voltage to the electrochromic units 111, 121 and 131 to properly adjust the reflectance of the mirrors according to the intensity of the rearward light. This conventional electrochromic rearview mirror system, in spite of further reducing unnecessary operation cycles of the electrochromic units, still has the problem of the narrow detection range. In other words, the glare resulting from the right rear side or left rear side is possibly not detected, and still stimulates the driver's eyes.